The present invention relates generally to dual mode fuel injection systems, and more particularly to a fuel injector with individually moveable needle valve members.
Over the years, engineers have been challenged to devise a number of different strategies toward the goal of a cleaner burning engine. Experience has taught that various injection timings, quantities and rates have a variety of different desirable results over the complete operating range of a given engine. Therefore, fuel injection systems with a variety of different capabilities can generally outperform fuel injection systems with narrower capability ranges, at least in their ability to reduce undesirable emissions. For instance, the leap from mechanical control to electronic control in fuel injection systems has permitted substantially lower emissions in several categories, including but not limited to NOx, hydrocarbons and smoke.
One area that appears to show promise in reducing undesirable emissions is often referred to as homogenous charge compression ignition (HCCI). In an HCCI engine, fuel is injected early in the compression cycle to permit thorough mixing with cylinder air, to ideally form a lean homogeneously mixed charge before conditions in the cylinder cause auto-ignition. Engines operating in an HCCI mode have shown relatively low outputs of undesirable emissions. Although an HCCI strategy appears promising, it has its own problems. For instance, HCCI can cause extremely high cylinder pressure rise rates and force loads, rendering it most desirable at the lower half of the engine""s operating range. Many are also seeking ways to address the difficulty in controlling ignition timing in engines operating with an HCCI strategy. Thus, at this time, a pure HCCI strategy is not viable for most commercial engine applications with conventional power density requirements.
This limitation of HCCI engines has been addressed in the art by equipping an engine with an HCCI fuel injection system and a conventional fuel injection system. For instance, such a dual system is shown in U.S. Pat. No. 5,875,743 to Dickey. Although such a dual system strategy appears viable, the high expense and complexity brought by two complete injection systems renders it commercially challenged. A single fuel injector is generally not compatible with performing both HCCI and conventional injections because different spray patterns are often desirable and sometimes necessitated. Providing a structure in a single fuel injector that is capable of injecting fuel in two different spray patterns, while maintaining the ability to mass produce the fuel injector and retain consistent results, has been problematic and elusive.
The present invention is directed to one or more of the problems set forth above.
In one aspect, a fuel injector includes a first needle valve member at least partially positioned in an injector body, and a second needle valve member at least partially positioned in the first needle valve member. At least one of the injector body, the first needle valve member and the second needle valve member define a high pressure space, a first nozzle outlet set and a second nozzle outlet set, a first needle control chamber and a second needle control chamber. The first needle valve member has a closing hydraulic surface exposed to fluid pressure in the first needle control chamber, and the second needle valve member has a closing hydraulic surface exposed to fluid pressure in the second needle control chamber. Each of the needle valve members is moveable individually while the other needle valve member remains stationary.
In another aspect, a method of injecting fuel includes a step of injecting fuel through a first nozzle outlet set at least in part by relieving pressure in a first needle control chamber. Fuel is injected through a second nozzle outlet set at least in part by relieving pressure in a second needle control chamber. Each of the two injection steps are performed at least in part by moving one of a first and second needle valve member while the other of the first and second needle valve member remains stationary.